Change of Magnetic Properties and Structure in Fe<SUB>3</SUB>O<SUB>4</SUB> Films on Si Substrates with Annealing Temperature

Abstract

We have investigated the magnetic properties and structure of Fe 3 O 4 films on Si substrates before and after annealing at various temperatures, T a . The saturation magnetization and the coercivity in the Fe 3 O 4 films are observed at all T a . They markedly increase with increasing T a up to 873 K, and their values become maximum at T a ¼ 873 K. Furthermore, they slightly decrease above T a ¼ 873 K. The Fe 3 O 4 phase mainly exists in the films at all T a . In addition, the -Fe 2 O 3 phase (hematite) is also formed in the films above T a ¼ 873 K. On the basis of these results, it is found that the growth of Fe 3 O 4 phase by annealing is mainly dominant in the change of magnetic properties in the Fe 3 O 4 film up to T a ¼ 873 K and that the formation of -Fe 2 O 3 phase influences the change of magnetic properties in the Fe 3 O 4 film above T a ¼ 873 K.

A Discovery of Strong Metal–Support Bonding in Nanoengineered Au–Fe3O4 Dumbbell-like Nanoparticles by in Situ Transmission Electron Microscopy

“…Accompanying the reduction of Fe, a shift in the Au 4f 7/2 peak from 83.8 to 84.2 eV is seen, as shown in Figure b. This +0.4 eV chemical shift can be explained either by a size effect (in our case, morphological changes observed in TEM) or by gold coordinating with iron forming an intermetallic phase, a similar shift as observed in the Au x In y alloy system …”

“…Accompanying the reduction of Fe, a shift in the Au 4f 7/2 peak from 83.8 to 84.2 eV is seen, as shown in Figure 3b. This +0.4 eV chemical shift can be explained either by a size effect 40 (in our case, morphological changes observed in TEM) or by gold coordinating with iron forming an intermetallic phase, a similar shift as observed in the Au x In y alloy system. 41 This XPS result indicating the surface reduction of the nano-Fe 3 O 4 hints at a fundamentally new phenomenon in metal/ oxide nanoscience, involving a cooperative size-and metalinduced reduction of oxide nanoparticle surfaces.…”

“…This XPS result indicating the surface reduction of the nano-Fe 3 O 4 hints at a fundamentally new phenomenon in metal/oxide nanoscience, involving a cooperative size- and metal-induced reduction of oxide nanoparticle surfaces. According to Syed et al, a 100 nm thick Fe 3 O 4 thin film deposited on Si substrate was completely stable against the reduction in the vacuum annealing (from 573 to 973 K at 9.75 × 10 –7 Torr) and therefore, the Fe 2p3/2 peak in the XPS spectra remained on the same binding energy. Also, a characteristic peak indicating a metallic Fe has never appeared .…”

“…According to Syed et al, a 100 nm thick Fe 3 O 4 thin film deposited on Si substrate was completely stable against the reduction in the vacuum annealing (from 573 to 973 K at 9.75 × 10 –7 Torr) and therefore, the Fe 2p3/2 peak in the XPS spectra remained on the same binding energy. Also, a characteristic peak indicating a metallic Fe has never appeared . This suggests that the spherical nano-Fe 3 O 4 has a higher reducibility and a higher capability of containing oxygen vacancies on its surface compared to flat extended Fe 3 O 4 .…”

“…Also, a characteristic peak indicating a metallic Fe has never appeared. 40 This suggests that the spherical nano-Fe 3 O 4 has a higher reducibility and a higher capability of containing oxygen vacancies on its surface compared to flat extended Fe 3 O 4 . As already observed from in situ STEM-EELS, the SMSB and the gold wetting behavior are closely related to the surface reduction of Fe 3 O 4 .…”